The present invention relates to a totally integrated system for transporting and converting geothermal and solar energy cooperatively into mechanical and electrical energy by more efficient means. Although means have been developed for utilizing geothermal energy or solar energy independently to produce heat and electricity, no sufficiently efficient system has been developed cooperatively utilizing the features of these two energy sources.
Exemplary disclosures showing geothermal and/or solar powered energy conversion systems include:
Merz; U.S. Pat. No. 1,493,368 PA1 Gill; U.S. Pat. No. 1,993,213 PA1 Biggs; U.S. Pat. No. 2,593,963 PA1 Walker; U.S. Pat. No. 2,720,489 PA1 Sauter; U.S. Pat. No. 2,820,548 PA1 Benedek et al; U.S. Pat. No. 2,933,885 PA1 Poldony; U.S. Pat. No. 3,070,703 PA1 Hughes et al; U.S. Pat. No. 3,459,953 PA1 Anderson; U.S. Pat. No. 3,846,986 PA1 Russel et al; U.S. Pat. No. 3,868,823 PA1 Hutchinson; U.S. Pat. No. 3,845,627 PA1 Martin et al; U.S. Pat. No. 3,950,949 PA1 "there are many geothermal reservoirs (perhaps 80% of all hydrothermal reservoirs) in which the temperature is not high enough to provide fluids that may be used with existing technology to produce economic power." Geothermal Energy, A National Proposal for Geothermal Resources Research, at page 43, available from the Superintendant of Documents as stock number 3800-00163. PA1 " . . . a great deal of heat of moderate potential is thrown away (possibly as much as is contained in the steam). . . . Discarding boiling water, from which power could be developed, may appear inherently wasteful but the decision is governed by economics. Clearly to utilize the water at the wellhead would entail a multiplicity of small power plants. (emphasis added).
Each of these energy conversion systems suffers from one or more of the following inherent disadvantages. Those systems relying solely upon the capture of solar rays as their natural energy source require the dedication of large areas of land to support the collector farms necessary to capture sufficient quantities of solar energy. Such land areas are not always available in sufficiently close proximity to the community to be served. The operation of such systems is also totally dependent upon the receipt of adequate sunlight by the collector array and must be supplemented by energy storage facilities or fueled auxiliary heat generators of large capacity at night and during other periods of inadequate sunshine.
Energy conversion systems that rely solely upon geothermal energy as their natural energy source, because of the relatively low temperatures obtainable from most geothermal wells, must normally also include provisions for the substantial addition of fueled auxiliary heat, in this case to raise the temperature of a fluid medium circulating through the geothermal source to a more readily usable level. The utilization of such auxiliary heat generators is exemplified by the furnace of the solar system disclosed by Ketchum and the gas-fired heater of the geothermal system disclosed by Paull.
All energy conversion systems, including those which combine geothermal and solar energy, fail to utilize efficiently the available geothermal energy thereby precluding use of a large percentage of potential geothermal resources. By way of background pertinent to this basic problem, the following quotation is taken from the findings of the Geothermal Resources Research Conference held in Seattle, Washington on September 18-20, 1972 and funded by the National Science Foundation (NSF):
The foregoing low-temperature problem primarily arises from the fact that prior art devices have heretofore failed to provide geothermal energy transport systems capable of delivering substantially all of the "wellhead" low temperature geothermal energy over extended distances without substantial energy loss. In this connection, it is important to note that the plurality of well-heads of many geothermal reservoirs are geographically dispersed such as to be spaced from one another by distances of up to 20 miles. Accordingly, to use many of the available geothermal resources, known energy conversion systems would necessarily entail the use of small, decentralized electrical power generating plants each in close proximity to a respective low-temperature fluid-dominated geothermal well so as to prevent high conduit heat loss, which would otherwise occur if geothermally heated fluid mediums from multiple geographically dispersed geothermal wells were pumped to larger and more efficient central power generating plants. Even in those situations where useable geothermal energy may be obtained in the form of naturally heated steam that might be present at the wellhead of a particular high-temperature geothermal resource, it is general practice to discard at the wellhead any boiling water that might also be present because of the economics involved with the utilization of the water as an energy source. The consequence, according to Geothermal Energy, Review of Research and Development, a 1973 publication of the United Nations Educational, Scientific and Cultural Organization (UNESCO), at page 118, is that:
It will therefore be seen that the failure to provide efficient transport systems for conducting a geothermally-heated fluid medium to centralized power generating plants and other thermal power stations without unacceptable geothermal heat loss en route either precludes use of many low-temperature, water dominated geothermal resources, or necessitates the inefficiency of locating small thermal stations at each wellhead which is usually also unacceptable.